17th Annual Terra Conference St. Paul, Minnesota – February 14, 2013
Top 10 Considerations for Designing, Constructing & Maintaining Long-Life
Concrete Pavements
Shiraz Tayabji Fugro Consultants, Inc., Columbia, MD FHWA ACPT Program Team
Ø Introductory Ø Top 3 Design Considerations
o Focus on Design Features o Joint Load Transfer o PCCP Support Condition/Drainage
Ø Top 5 Construction Considerations o Construction Quality
§ Poor Design/Quality Construction vs. Good Design/Poor Construction
o Concrete Management – from Plant to Curing o Well-developed Specs/End Product Emphasis o Contractor Process Control o Agency Acceptance Testing
Presentation Outline
Ø Top 2 M&R Considerations o Timely M&R o Accelerated M&R (to Minimize Traffic
Congestion & Improve Work Zone Safety
Presentation Outline (Cont.)
Simply by Achieving Consistently What We Know is Attainable
& Continue Making Concrete
Pavements Cheaper & Sustainable (in terms of overall LCA) by Taking Advantage of
New Developments
HOW CAN WE GET THERE?
Ø Original PCC surface service life – 40+ years Ø Pavement will not exhibit premature failures
and materials related distress o Pavement failure=> Result of traffic loading
Ø Pavement will have reduced potential for cracking, faulting & spalling, and
Ø Pavement will maintain desirable ride and surface texture characteristics with minimal intervention activities to correct for ride & texture, for joint resealing, and minor repairs
US Expanded Definition of Long-Life Concrete
Pavements
Current PCCP Hot Topics Ø Design o MEPDG implementation o Optimizing design features o Composite pavement (PCC(+)/PCC(-) for new) o Precast pavement (rapid rehab/reconstruction) o In with the old – CRCP getting more attention
Ø Materials (major focus: durability & sustainability) o Dense (well) graded aggregates (3+ sizes) o Less cement use, more SCM (flyash & slag) o Two-lift paving (PCC(+)/PCC(-) ) o Joint concrete durability (joint rot issue)
Current PCCP Hot Topics Ø Construction
o Jointing § Single vs. double cut; sealing vs. no-sealing § Dowel bar alignment testing & specification
o Two-lift paving o Stringless paving o End product specification/PRS o Pro-active contractor process control
§ Concrete testing; profile testing
Ø Repair/Rehabilitation o Rapid/Accelerated
§ Full closures vs. night/weekend closures o Thin concrete overlay use o Precast pavement use
Current PCCP Hot Topics Ø Surface characteristics/user benefits o Reduce wet weather accidents o Improve ride o Reduce pavement/tire noise
Ø Construction management o Minimize extended lane closures o Reduce congestion o Reduce work zone accidents
Ø US FHWA national focus areas o Recycling
Top 3 Design Considerations
• Focus on Design Features • Load Transfer at joints • PCCP Support Condition/Drainage
1 - Comprehensive Long-Life Concrete Pavement Design
Ø More than just slab thickness Ø Incorporation of appropriate design features
to enhance performance (e.g., improved base, dowel bars, etc.)
Ø Must design pavement as a system o Consider interactive effects of all design
elements o Consider overall cost effectiveness o Consider use of locally available & recycled
materials
1 - Comprehensive Long-Life Concrete Pavement Design
Ø Some simple changes in approach to reduce concrete volume & amount of other materials without compromising performance o Reduce slab thickness
§ Improve foundation/base (European approach) § Use widened lane & shorter joint spacing
o Reduce materials § Reduce no. of dowel bars (9 or 10 vs.12 per lane) § Reduce joint sealant material (single cut sawing)
Ø Other changes o Consider two-lift design & construction to allow use of
local/marginal & recycled materials in the lower lift.
2 - Joint Load Transfer —
Ø Joint spacing – Typical practice o 15 ft (4.6 m) max for most
highway applications o Uniform spacing & perpendicular
joints Ø Load transfer (40+ year design)
o Corrosion protection a must § Epoxy-coated (?) § Clad bars (steel/zinc) § Microcomposite steel (MMFX) § Fiber-reinforced polymer (FRP)
2 - Joint Load Transfer
Ø Dowels for truck-loaded highways, typically for § Slab t > 8 in or ESALs > 5 million § Minimum 1.25 in (32 mm) diameter
Ø Round dowels meet needs & are economical Ø Need to maintain LTE at joints - > 70% Ø NO NEED FOR MIDDLE 2 to 3 BARS IN
EACH LANE
3 – Support Condition/Drainage Ø US Approach – Do the best we can? Ø European approach – Start with a good (standard)
foundation Ø We must construct better support – cannot undo
poor support in future R&R Ø Non-erodible base - prevention of pumping Ø Stiffer support - reduction in slab stresses &
deflections; less rolling resistance (MIT study) Ø Provide stable and uniform construction platform
– achieve better concrete surface finish Mentality switch – Refer to a base as a base
& not as a subbase
3 – Support Condition/Drainage Base Type Selection
Ø Provide for needed base-slab friction Ø Provide for needed frost heave protection Ø Provide for needed subsurface drainage Ø Untreated granular (aggregate) bases should be
reserved for low traffic Ø Stabilized (treated) bases for LLCP (40+ years)
o Asphalt-treated/Cement-treated o Lean concrete bases (Caltrans use) o Permeable bases – treated
3 – Support Condition/Drainage Pavement Subsurface Drainage
Ø Need to pay more attention Ø Rapidly remove water from
beneath pavement structure o Stability vs. porosity: use lower
permeability material <300 - 500 ft/day (90 - 150 m/day)
Ø Drainable Pavement System o Daylighted permeable base o Permeable base with edge
drainage system
Top 5 Construction Considerations
• Construction Quality • Poor Design/Quality Construction vs. Good
Design/Poor Construction • Concrete Management – from plant to joint
sawing • Well-developed Specs/End Product
Emphasis • Contractor Process Control • Agency Acceptance Testing
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Ø For construction projects, achieving quality equates to conformance to requirements o Requirements need to be well defined, can
be measured, and are not arbitrary Ø Quality must be built into a project. It is
not a hit or miss proposition.
4 - Construction Quality?
• Owner should not expect more than what
is specified
• Contractor may not deliver more than what is specified
Poor Design/Quality Construction vs. Good Design/Poor Construction
A poorly designed pavement but well constructed will outlast a well designed pavement but
poorly constructed Ray Rollings
Retired, Corps of Engineers
4 - Construction Quality?
5 – Concrete Management Ideal Paving Concrete Mixture
Ø US vs. European approach (Freeways) o US: ~650 psi MR & slab t = 12 to 14 in. o European: 750+ psi & slab t = 10 in.
Ø Design for low paste - most concrete durability concerns are due to paste issues o Results in better slipform paving & better finishing
Ø 2-lift paving – Top: PCC(+); Bottom: PCC(-)
5 – Concrete Management The Joint Rot Issue
Ø Some joints are deteriorating faster than we would like (Peter Taylor)
Ø Some key findings o Paste saturation is a main culprit (f(freeze/thaw)) o Need better quality concrete – w/cm < 0.40 & good in-
situ air system & dense concrete & well-draining pavement, especially at the joint
5 – Concrete Management From Placement to Curing
Ø Proper consolidation o Use of smart vibrator system o Check cores for proper consolidation
Ø Minimize tendency to over-finish surface o Brings more paste to the surface o Surface does not have to be super-smooth
Ø Timely curing o A concern on many projects during hot weather
Ø Timely & proper joint sawing o Not an issue for transverse sawing, but delay in
longitudinal sawing can result in premature cracking
6 – Well-Developed Specs Construction Specification Objective
Ø To identify and accommodate or minimize variability in the concrete pavement construction process o To deliver an end product that is durable o To minimize risk of premature failures o To minimize owner’s risk of accepting a marginal
product o To minimize contractor’s risk of rejection of an
acceptable product
Good Specs lead to Good Construction!
Ø Ideal contractor process control (QC) limits or eliminates placement of marginal concrete & use of marginal construction processes o Do not produce concrete if aggregate grad. not met o Reject concrete loads if requirements not met o Stop paving process if placement (edge slump) or
consolidation issues Ø Process control tests
o Aggregate gradation & concrete mixture o Slab thickness o Concrete “slump” & air & density/consolidation o Profile (behind paver) & texture o Dowel bar alignment
7 – Contractor Process Control
Ø Perform sufficient testing to verify marginal materials & construction techniques are not being used o Statistically based sample testing best o Preferably rapid nondestructive testing
Ø Test for end product metrics (PWL) o Slab thickness o Concrete strength o Concrete durability – air/denseness o Smoothness & texture o Dowel bar alignment (?) o Early age distress
8 – Agency Acceptance Testing Determine the Degree of Compliance
Ideal Testing Behind paver, not in front of paver
Top 2 M&R Considerations
• Timely Maintenance & CPR • Accelerated M&R
• Minimize Lane Closures & Traffic Congestion
• Improve Work Zone Safety
Ø We expect that current & future new concrete pavements will provide a low maintenance service life
Ø However, we still have to manage concrete pavements constructed more than 20 years ago & designed for ~20+ years. Many of these pavements have been in place for 40+ years.
Ø With timely M&R strategies, we can continue to extend the service life of many of these older concrete pavements without resorting to “fracturing” & reconstruction o Economical & sustainability benefits
M&R Overview
Ø With minimal effort and lower costs, we can extend service life of most concrete pavements without fracturing, resurfacing & reconstruction
Ø Well-performing CPR techniques are available – to maintain ride/texture/structural capacity
o FDR, DBR, grinding, concrete shoulder retrofit o Joint resealing ? – topic of debate
Ø But, M&CPR must be done in a timely manner & done well (NO MORE FIXING THE FIX)
9 – Timely M&CPR Extend service Life of Existing Pavements
Ø Take advantage of advances in repair materials o Rapid set concretes (cementitious binder) o Polymer-based materials o Other
Ø Consider precast pavement for full-depth repairs & rehabilitation o Production use by NYSDOT, NJDOT, Illinois Tollway,
Caltrans o Cost effective & longer-lasting
10 – Accelerated M&R Technologies Minimize Lane Closures & Traffic Congestion
& Improve Work Zone Safety
CA I-680 Precast Prestressed System Up to 36 ft long panels over new RSLCB, 2011
Achieving LLCP (40+ years) Many Small Steps => Big Gains (LLCPs)
One Small Misstep => Premature Failure (PPCPs)
Ø Optimizing long-life pavement designs o Thickness reduction; fewer dowel bars o Single cut joints; better bases/foundation
Ø Managing the construction processes & materials
Ø Effectively extending service life of existing pavements by timely M&CPR
